Odds favour warmer than average winter

The Bureau’s winter temperature outlook shows the odds for a
warmer than average season are better than 50:50 over the entire
country for both daytime and nighttime temperatures. The strongest
swings in the odds are over the west and north of Australia.

For the June to August period the chances of above average
seasonal daytime temperatures are over 60%
across WA, the NT, most of Queensland and north and west SA. The
highest probabilities are in western WA where they approach 80%.
These probabilities have resulted from
higher than average sea
temperatures in the tropical Indian and western tropical Pacific
Oceans.

So with climate patterns like the current, about 6 to 8 winters
out of every 10 are expected to be warmer than average across the
west and north of Australia, with about 2 to 4 out of 10 being cooler.
The Bureau’s winter maximum temperature outlooks have
moderate reliability over much of the
country (see background).

The chances of above average seasonal minimum temperatures
are between 60 and 80% across WA, the NT,
Queensland and parts of northern NSW. Minimum temperature outlooks
for winter have moderate to high
reliability over the southern half of WA, Queensland, much of NSW and
the east of the NT.

These outlooks are for the average maximum and minimum
temperatures for the entire outlook period. Information about
whether individual days or weeks may be unusually hot or cold, is
unavailable.

This outlook uses data from both the
Pacific and Indian Oceans.
The Pacific has been cooling but remains warm in the west, whilst
the Indian is warmer than average over large areas.

Model Reliability:
Strong reliability means that tests of the model on historical data
show a high correlation between the most likely outlook category
(above/below median) and the verifying observation (above/below median).
Low reliability means the historical relationship is weak.

This outlook represents a summary: more detail is available from the contact
people or from SILO.

Important: Probability outlooks should not be used as if they were categorical
forecasts. More on probabilities is contained in the booklet "The Seasonal Climate
Outlook - What it is and how to use it", available from the National Climate Centre.

For more information regarding this outlook please contact the
following climate meteorologists in the
National Climate Centre from 9:00am to 5:30pm (EST) Monday to
Friday:

A:General statements about the
probability or risk of wetter or drier than average weather over a
three-month period. The outlooks are based on the statistics of chance
(the odds) taken from rainfall and sea surface temperature records. They
are not, however, categorical predictions about future rainfall, and
they are not about rainfall within individual months of the three-month
outlook period.
Q: WHAT DO WE MEAN BY WETTER OR
DRIER THAN "AVERAGE", OR WARMER OR COOLER THAN "AVERAGE"?

A:Being above or below the MEDIAN rainfall,
MEDIAN maximum temperature, or MEDIAN minimum temperature over the three-month
outlook period.
The median is the middle value in the historical record for the period in
question. In the long term, rainfall or temperature are above median in one
half of years, and below median in the other half.Example 1: For the July to September period at Mackay in Queensland, one-half
of 3-month rainfall totals have been below 80mm, and one-half have been above.
If rainfall was above 80mm in that period it would be "wetter than average" or
above median. Over the long haul there is a 50% chance of this occurring.
In terms of odds this is even money.Example 2: In Sydney, one-half of summers (Dec-Feb) have a mean
maximum temperature above 25.7°C, with the other half being below.
Therefore 25.7°C is the median.
Note that the mean or average maximum temperature is the
average of all the daily highest temperatures for the period.
Similarly, the mean or average minimum temperature is the
average of all the daily lowest temperatures for the period
Q: HOW ACCURATE ARE THE OUTLOOKS?

A: In the places and seasons
where the outlooks are most skilful, the category of the eventual outcome
(above or below median) is consistent with the category favoured in the
outlook about 75% of the time. In the least skilful areas, the outlooks
perform no better than random chance or guessing. The rainfall outlooks
perform best in eastern and northern Australia between July and January,
but are less useful in autumn and in the west of the continent. The skill
at predicting seasonal maximum temperature peaks in early winter and drops
off marginally during the second half of the year. The lowest point in skill
occurs in early autumn. The skill at predicting seasonal minimum temperature
peaks in late autumn and again in mid-spring. There are also two distinct periods when
the skill is lowest - namely late summer and mid-winter. However, it must
always be remembered that the outlooks are statements of chance or risk.
For example, if you were told there was a 50:50 chance of a horse winning
a race but it ran second, the original assessment of a 50:50 chance could
still have been correct.
Q: WILL CATEGORICAL OUTLOOKS EVER BE
ISSUED? (Eg. It WILL be drier than average.)

A: Very unlikely. There is a certain
level of natural variability in the climate which is chaotic and unpredictable.
This is particularly the case with rainfall. For example, rainfall in a
season can be significantly above average in one region, and significantly
below average less than 50km away.
Q: HOW SHOULD THE OUTLOOKS BE USED?

A: As another tool in risk management
and decision making. The benefits accrue from long-term use, say over 10
years. At any given time, the probabilities may seem inaccurate, but taken
over several years, the advantages of taking account of the risks will
outweigh the disadvantages. For more information on the use of probabilities,
farmers could contact their local departments of agriculture or primary industry.

The SOI is one indicator of the stage of El Niño or La Niña events
in the tropical Pacific Ocean. It is best considered in conjunction with
sea-surface temperatures, which form the basis of the outlooks.

A strongly negative SOI (below -10) is characteristic of El Niño, which is
often associated with below average rainfall over eastern Australia, and a
weaker than normal monsoon in the north.

A strongly positive SOI (above +10) is characteristic of La Niña, which is
often associated with above average rainfall over parts of tropical and
eastern Australia, and an earlier than normal start to the northern monsoon
season.
El Niño &
La Niña

El Niño translates from Spanish as "the boy-child", and refers to
the extensive warming of the central and eastern Pacific Ocean.

La Niña translates from Spanish as "the girl-child", and refers to
the extensive cooling of the central and eastern Pacific Ocean. The term has
recently become the conventional label for the opposite of El Niño.